6sl7 front end

[passfan]

it was for personal taste. Just trying to make up for some of the loss in using 6sl7's

I thought there might be an impedance issue, thanks.

[passfan]

Octal twin triodes can be noisy, hence the DC filaments. There is still plenty of gain even without another gain stage. You may also have to weed through a bunch of tubes to get non-microphonic, usable tubes.

I've got a handful of russians and a few JAN6188 from 86' NOS.

[Cliff Schecht]

Octal twin triodes can be noisy, hence the DC filaments. There is still plenty of gain even without another gain stage. You may also have to weed through a bunch of tubes to get non-microphonic, usable tubes.

Also make sure to connect the shield to either ground or one of the cathodes. I did a harp amp with a 6SJ7 pushing an Express type second and third gain stage and found that it picked up all kinds of crap (radio and oscillations) until I connected the metal casing to the cathode.

[passfan]

I know it's been a while but..."ITS ALIVE!!!!"

I used Aikens PI but the rest of the front end is Rocket. I have a slight hum issue but it sounds nice.
There are some things to work out:

) The gain is low. It has no breakup. It's like stopping your volume just before it breaks, level wise.
) I had to cut out the P.I.G. It didn't like that at all
) The B+ is around 412...might have to play with that but the PT gets warm. It feels really loaded. I guess 6sl7's draw a lot of current.

Any more suggestions would be welcome.
The sound is like having cream on top of your rocket. It would make a great blues amp just as it sits, I'm just sure it could be better.

[dartanion]

Change the CF to a clipping stage like the Express or Liverpool. Much more gain that way.

[passfan]

Change the CF to a clipping stage like the Express or Liverpool. Much more gain that way.

That's what I slept on last night and you're right. I used dc on the heaters and I think I forgot to reference the negative side to ground. That will probably help out with the hum problem.

[funkmeblue]

shielding the first 6sl7 rids alot of the noise. It's not easy to find a nice quiet 6sl7. I borrowed the shield from some old p.a. equipment that had 6sl7's in it. I think the rocket is a lot cleaner amp anyway, convert it to express specs. I've been thinking about adding the cathode follower at the end like the concorde, sounds fun

[passfan]

Perhaps I'll utilize the extra triode for another gain stage and leave the cf to buffer into the tone stack.

[funkmeblue]

alessandro uses a 6sn7 for the 3rd gain stage in his redbone amp.

[lumox0013]

any chance for some gut shots,i've been wanting to do something like this for a while i would love to see.please and thank you

[M Fowler]

Ground the first octal preamp tube bias resitor/cap to the input jack to reduce hum and noise.

Mark

[funkmeblue]

instead of going to the ground bus? How does that make a difference?

[passfan]

any chance for some gut shots,i've been wanting to do something like this for a while i would love to see.please and thank you

I will first chance I get. It's pretty much a prototype in an old organ chassis, a mess of jumbled you name it , and it will be that way until I've tweaked all the bugs out or toss it aside.

[passfan]

Well here are some things tried.
) tried to utilize the extra triode in V2A as a gain stage to drive the CF in V2B to feed into the tone stack and failed. Not sure why but I could only get a faint signal through at full volume.
) dropped the CF and went with the gain stage in V2A and it sounded great until around half volume and up and then it started farting out. The higher the volume the worse it got so I went back to the CF.
) decided to remove the dc supply to the heater and reference the 33 volts cathode bias on the output to no effect. Nothing better, nothing worse, no change.
) grounded the first stage bias to the input shield at the cliff jack to no effect on the 60 hz hum but it did add a nice mid frequency buzz. I've yet to reverse that.
) started swapping out nos jan 6sl7's and what a difference from the old cheap russians I have. Dropped some el34's in the output and this thing is transformed. It perked up a bit breaking up now around half volume and the volume is deceiving. I didn't think it was loud yesterday because I'm not used to 6sl7's.

I wonder how much effect on the hum my old steel chassis is having on this curcuit plus the chassis comes in two halves and they're bolted together. A lot could go wrong with the return path. I'll keep fiddling but it sure is fun to play.

As always suggestions welcome.

[M Fowler]

Your just eliminating the noisey chassis path from input to cathode by wiring the bias resistor/cap directly to the input jack for low level signal ground. I do this on my PTP builds.

On a turret board build most are already tying the input jack to the buss bar.